Products obtained from plants form an important part of the economies of many (even perhaps most) states and countries. While an exhaustive list may fill several pages, examples include grains, lumber, nuts, fruits, vegetables and the like.
Often, such products are used by buyers foreign to the political jurisdiction in which the product is grown.. Of necessity, such products must be shipped across political boundaries, perhaps several such boundaries while moving from such site to the place where the product is finally used.
For example, the States of Georgia, California, Florida and Texas and the countries of Mexico, Brazil and Guatemala (to name just a few) have substantial agricultural economies. Products grown within those jurisdictions may be shipped all over the world. And, similarly, those states and countries receive agricultural products from other jurisdictions.
One of the risks arising from such "inter-jurisdictional" trade is that an aspect of the local agricultural industry may be endangered, perhaps critically endangered, by animals infesting the product or by crop diseases carried by such animals. As used in this specification, the term "animals" means insects larvae or adult form), mammals (e.g., rats and mice), reptiles and/or birds.
Such animals may and frequently do infest the product at the site of packing and/or during transit and unless precautionary steps are taken, great harm can come to an agricultural economy to which the animal or the disease is foreign. Under those relatively narrow circumstances, the aforementioned animals must be considered as pests. Merely as an example of the type of precaution commonly taken (evidence of the potential seriousness of the problem), motorists travelling between Canada and the United States or into certain states in the United States are routinely asked whether they are carrying fruits or vegetables or certain types thereof which may carry vegetable disease.
As a result of such commonly-occurring product animal infestation, states and countries take special precautions to assure that animals "hitchhiking" in products crossing political boundaries are killed before entering the jurisdiction so that they cannot directly or indirectly impair the local agricultural industry. Animal exterminating may be carried out at the boundary itself or at loading, unloading or storage points enroute.
It is also to be appreciated that pests indigenous to a jurisdiction may contaminate a product. In fact, the inventive method and apparatus find greatest utility in killing indigenous insect pests in food products since live pests are considered to be food contaminants.
A commonly-used approach is to fumigate the load of product, which may be transported by rail car, over-the-road semi-trailer, ship or the like. Loads in rail cars or semi-trailers are typically fumigated by first sealing cracks and openings in the car or trailer as well as reasonably possible. Complete sealing is not practically possible. Then a can of methyl bromide, a commonly-used fumigant, is opened and tossed into the car or trailer. The doors are closed and the fumigant left to diffuse through the product.
A somewhat similar approach is commonly used with bagged, shipborne products such as cocoa and coffee beans. The bags are unloaded to the dock, covered with a tarpaulin and one or more open cans of methyl bromide placed beneath the tarpaulin and left to diffuse through the product.
However, treating the load with, e.g., methyl bromide is not the end of the process. After the fumigant has presumably fully diffused through the product and killed any animals therein, the load must be ventilated or permitted to ventilate to remove all traces of the fumigant which is poisonous to humans and other types of life.
And the effectiveness of the process can only be determined by inspection. Experience has demonstrated that such processes, which are fairly described as being a bit haphazard, are sometimes less than fully effective in killing all animals present in the load.
Another, less-commonly-used process involves placing the load in a large container vessel, sealing the vessel and releasing a poison gas fumigant into the vessel load is then held in the sealed vessel until the gas fully diffuses throughout the load, killing animals which may be present. Following animal extermination, the is ventilated for the reasons mentioned above.
Examples of apparatus in this general field are depicted in U.S. Pat. Nos. 1,501,958 (Mackie); 1,725,650 (Kobilke); 4,239,731 (Gillis et al.) and 4,944,919 (Powell). The process described in the Mackie patent is said to be useful in destroying animal life in fabrics, food products, hides and plants. In such process, a product is placed in a shell, the shell sealed and the pressure in the shell reduced below atmospheric ambient pressure.
A mixture of air and a fumigant, carbon disulphide, is then introduced into the shell, being drawn thereinto by the partial vacuum. Such introduction causes the pressure in the shell to rise to about atmospheric ambient and the product is held in the shell for a period of time. The patent states that such time may be "sixty minutes or in some cases longer" but there is no clue to the volume of the load or to what specific types of products may be treated.
The process described in the Kobiolke patent also involves placing "food products" or "other material" in a kiln and reducing the kiln pressure below atmospheric ambient to partially remove oxygen. As further described in such patent, the partial vacuum is then used to introduce carbon monoxide to absorb additional oxygen the kiln pressure rises to ambient pressure as a result of such introduction. The kiln pressure is again reduced and carbon bisulphide is introduced to destroy insect pests. Then air is permitted to rush into the kiln and such air (along with circulating fans) cleanses the material being treated. Presumably, this means the material is ventilated until free of poisonous carbon bisulphide.
While the foregoing processes have been the best available until the invention, such processes are attended by certain disadvantages. Some of these are readily apparent and some are not so apparent.
An obvious disadvantage is that all of the aforementioned processes use poisonous gas fumigants. Unless the product is thoroughly ventilated, traces thereof may linger to be later consumed by humans and animals. Another obvious disadvantage is that in many instances, the fumigant is simply allowed to dissipate in the air with consequent pollution of the environment. And certain fumigants are known to deplete ozone.
A less-apparent disadvantage--but one which dramatically influences the time required to carry out the known processes--is that because there is little of no air movement within the load being treated, the poison gas fumigant must propagate through such load by diffusion. Diffusion is slow; it is common to require six to forty-eight hours for complete fumigant diffusion in a large load. An animal exposed to a fumigant may be killed after a few minutes of exposure but it may take a day or two for such fumigant to propagate deeply into the interior of the product load to reach the animal.
The long time required is especially true with loads of "dense" products, i.e., those having only a few, very small interstices. Baled tobacco, stacked lumber and the like are examples of products having very little air space between individual product constituents.
Yet another disadvantage is that such processes may or will, as a practical matter, be prohibited in the near future. Methyl bromide is being banned by the U.S. Environmental Protection Agency and the use of other popular fumigants may be severely restricted.
Still another disadvantage is that at least as to the process described in the Kobiolke patent, multiple gaseous constituents are needed to carry it out. This results in unnecessary constituent storage and handling.
Yet another disadvantage of the prior art processes is that they are not entirely reliable in killing all animals present within a "batch" of products. This is especially true of products like coffee and cocoa beans treated as described above. At least at the edges of the stack, air is likely to seep in and impair or destroy the effectiveness of the fumigant. Consequently, product inspections must be carried out--and it is left to the imagination to say how one readily inspects the interior of a bag of cocoa beans.
An improved method and apparatus which materially shortens process time, which can be carried out without the use of fumigants, which can avoid the need for product ventilation and which avoids environmental pollution would be an important advance in the art.